MYOGLOBIN AS AN ULTRASTRUCTURAL PROBE FOR STUDYING PERMEABILITY OF THE NEPHRON

The potential of myoglobin as a nontoxic ultrastructural probe for endothelial permeability, as a tracer for studying cellular uptake and transport, and as a protein tag for immunocytochemical experiments is enormous. An ellipsoid molecule with a Stokes-Einsten radius of 17A, the myoglobin molecule undergoes rapid molecular sieving through the glomerular barriers and flows rapidly into the urinary fluid. Bulk flow through the glomerulus results in the saturation of the proximal endocytic apparatus and in the translocation and concentration of myoglobin within the lumen of the distal segments of the nephron. The distal segments of the nephron lack an active endocytic apparatus and are thus unable to reabsorb lumenal myoglobin. This results in the formation of epithelial casts necrosis of some epithelial cells and in proteinuria.